Lowther LL18S stereo power amplifier - circuit diagram?

[EC8010]

Does anyone have a circuit diagram or known valve complement for this amplifier?

[James D.]

Hello EC8010,

No luck hunting down the LL18. Do you have any info. on it at all?

One of my valve mentors back in the sixties had an LL10 but his home designed amps were better.

Found an Italian web page with some nice old Lowther amp. ads.

Lowther amp ads .

ciao

James

[EC8010]

Hello James,

Jonathan Hill's "Audio! Audio!" gave the following information:

LL18S stereo valve amplifier (1970/75), power output 18 Watts per channel, ultra-linear, output valves EL506, input sensitivity 750mV, output impedance 16 Ohms, harmonic distortion 0.1%, frequency response 20Hz-60kHz ±1dB, signal-to-noise level -85dB. Size 10½" x 11" x 8". Original price £47. (For use with MkII and SCU/T stereo control units.) Produced at a time when very few valve amplifiers were being manufactured.

The example I saw had a chromed chassis and had two ECC82 per channel. The thing is, Lowther tended to use Brimar valves (EL506 is Brimar) so ECC82 is a slightly odd choice, and I'm wondering if they really belong in there. I only had time for a quick look, so I couldn't trace out a circuit diagram. I'll have a photograph in a few days (once the film is developed).

Thanks for the link.

[fdegrove]

Hi,

If I recall correctly that amp used 13D3s (Brimar), not ECC82s.

Cheers,

[EC8010]

Originally posted by fdegrove
If I recall correctly that amp used 13D3s (Brimar), not ECC82s.

Hello Frank,

thank you! That's exactly what I suspected! ECC82 isn't Brimar, but 13D3 is, and if you were in a repair shop, the chances of them having 13D3 would be low, whereas ECC82 is common as muck, and would be a fairly reasonable replacement (although lower mu).

[fdegrove]

Hi,

Is the diagram of the LL26 of any use to you?

I think it uses more or less the same differential splitter with the penthode as a CS in the tail...

If you want it let me know and I'll e-mail it.
There's little point in resizing it and posting it here as it would likely become too hard to decypher.

Cheers,

[EC8010]

Originally posted by fdegrove
Is the diagram of the LL26 of any use to you?

Thanks, but I already have the LL26 diagram. the LL18S doesn't have a CCS, just a pair of double triodes. Might you have been thinking of the LL26 when you suggested 13D3? Knowing of the LL26, 13D3 was my first thought, you see...

[fdegrove]

Hi,

Might you have been thinking of the LL26 when you suggested 13D3? Knowing of the LL26, 13D3 was my first thought, you see...

Not really...I once had a customer with a LL18 and I'm pretty sure it used a 13D3 as well.
I could be wrong but I think it used it as a paraphase splitter with a EF86 in front?
Mind you this is really ages ago so, don't shoot me if I'm wrong.

If you can't find more info locally maybe Steve at Kiewa Valley can help you out:

DOWN UNDER...

If your unit uses Partridge iron it may be worth keeping...

Cheers,

[James D.]

Interesting stuff! I think I have some EL506s at home too...

How similar are the designs to Leak amps? How do they sound and were they optimised for Lowther speakers?

ciao

James

[EC8010]

Frank: EF86 and 13D3 paraphase plus push-pull EL506 sounds very similar to the Brimar VA11 20W amplifier in Brimar No10.

James: Odd you should mention Leak... The Brimar VA11 looks just like a Leak TL12+, right down to 120mV sensitivity for 20W output. I should see the Lowther LL18S in a few weeks' time, so this time I will take valve pin-out information and a piece of paper with me to trace out the circuit.